1. Field of the Invention
The invention relates to an optical fiber module.
2. Discussion of the Background
Optical components having the functions of beam splitting, optical switching, and wavelength multipelxing and demultiplexing have been widely used in optical communications. The optical components are formed variously, but among them, the optical components having an optical waveguide circuit in which a circuit formed of optical waveguides is formed over a substrate have been prospective in view of the integration and mass production.
Traditionally, the optical waveguide circuit has been formed in which the circuit of optical waveguides made of a silica-based material is disposed on a silicon or silica substrate. In recent years, however, the optical waveguide circuits have been also formed in which a substrate and an optical waveguide forming region are formed of polyimide-based materials.
FIGS. 10 and 11 are diagrams illustrating examples of the optical waveguide circuits. In the optical waveguide circuits, a waveguide forming region 10 is formed over a substrate 11.
FIG. 10 illustrates an exemplary configuration of the optical waveguide circuit formed with a 1xc3x978 waveguide beamsplitter as the circuit formed of optical waveguides. FIG. 11 illustrates an exemplary configuration of the optical waveguide circuit formed with a circuit of an arrayed waveguide grating as the circuit formed of optical waveguides. The arrayed waveguide grating is used for wavelength division multiplexing. Various circuit configurations have been proposed therefor.
As shown in FIG. 10, the 1xc3x978 waveguide beamsplitter has one input optical waveguide 12 and eight output optical waveguides 16. A plurality of splitting parts 17 are formed between the input optical waveguide 12 and the output optical waveguides 16.
As shown in FIG. 11, the circuit of the arrayed waveguide grating has at least one input optical waveguide 12, a first slab waveguide 13 connected to the output end of the input optical waveguide 12, an array waveguide 14 connected to the output end of the first slab waveguide 13, a second slab waveguide 15 connected to the output end of the array waveguide 14, and a plurality of output optical waveguides 16 arranged side by side that is connected to the output end of the second slab waveguide 15.
The array waveguide 14 transmits the light lead out of the first slab waveguide 13, which are formed to arrange a plurality of channel waveguides 14a side by side. The lengths of the adjacent channel waveguides 14a are varied at a set amount (xcex94L) each other.
The channel waveguides 14a forming the array waveguide 14 are usually disposed in plurals such as a hundred waveguides. The output optical waveguides 16 are disposed corresponding to the number of signal lights demultiplexed or multiplexed by the arrayed waveguide grating, for example, the signal lights have wavelengths different from each other. However, in FIG. 11, the numbers of each of the channel waveguides 14a, the output optical waveguides 16 and the input optical waveguides 12 are illustrated simply for simplifying the drawing.
For example, as shown in FIG. 11, when wavelength-multiplexed lights are lead into one input optical waveguide 12 in the circuit of the arrayed waveguide grating, the wavelength-multiplexed lights pass through the input optical waveguide 12, and they are lead into the first slab waveguide 13. Then, the wavelength-multiplexed lights spread by the diffraction effect of the first slab waveguide 13, enter the array waveguide 14, and transmit through the array waveguide 14.
The lights transmitted through the array waveguide 14 reach the second slab waveguide 15, and focus on the output optical waveguides 16 for output. However, the lengths of all the channel waveguides 14a of the array waveguide 14 are varied from each other, and thus a shift is generated in the separate light phases after transmitted through the array waveguide 14. Then, the phasefront of the focusing lights is titled according to the shift amount, and the tilted angle determines the focusing position. Therefore, the lights having wavelengths different from each other can be outputted from the different output optical waveguides 16.
For example, as shown in FIGS. 12A to 12C, an optical component 1 having the optical waveguide circuit with the circuit of the arrayed waveguide grating or the waveguide beamsplitter is housed inside a package 2, and it is used as an optical fiber module. FIG. 12A is a perspective view illustrating the appearance of the optical fiber module. FIG. 12B is a diagram of the optical fiber module that the inside is seen from above. FIG. 12C is a cross-section of a line Axe2x80x94A shown in FIG. 12B.
The optical fiber module shown in FIGS. 12A, 12B and 12C has a first optical fiber 3 (3a) and a second optical fiber 3 (3b). The first optical fiber 3 (3a) is connected to one end side of the optical component 1, and the second optical fiber 3 (3b) is connected to the other end side of the optical component 1. One end sides of the optical fibers 3 (3a and 3b) are connected to the optical component 1, and the other end sides are drawn out of the package 2. The optical fibers 3 (3a and 3b) are fixed to the package 2 with an adhesive 23.
The first and second optical fibers 3a and 3b are formed of optical fiber ribbons, for example, having a plurality of optical fibers arranged side by side. An optical fiber array 21 is disposed at the connection end face of the optical fiber ribbon. The connection of the first and optical fibers 3a and 3b to the optical component 1, that is, the connection of the optical fiber arrays 21 to the optical component 1 is fixed with the adhesive.
In addition, lids 20 are attached to the connection end faces of the optical component 1, which allow stable connection of the optical component 1 to the optical fiber arrays 21 at the end parts of the first and optical fibers 3a and 3b. 
The package 2 has a package main body 2a and a cover part 2b. The package 2 is mainly formed of metals such as aluminum and stainless steel or plastics. The package 2 houses the optical component 1 and the connecting parts of the optical component 1 to the optical fibers 3 (3a and 3b) inside the package 2, whereby protecting them.
The optical fiber module is supposed to be used in the temperature range from 0 to 70xc2x0 C., for example. Therefore, the optical fiber module is demanded not to vary the characteristics in the range of temperature for use. Accordingly, for the optical component 1 being greatly affected in the optical characteristics by temperature changes including the arrayed waveguide grating, temperature control is needed. Furthermore, the range of temperature for use in the optical fiber module is the range from xcx9c5 to 65xc2x0 C., 0 to 65xc2x0 C., and 0 to 55xc2x0 C.
Then, in the optical fiber module shown in FIGS. 12A to 12C, an optical fiber module having a temperature control device (not shown) disposed inside the package 2 is proposed. The optical fiber module adapts a method that the optical component 1 is heated and kept at constant values at temperatures of 70 to 80xc2x0 C., for example, by the temperature control device. For the optical fiber module disposed with the temperature control device, it is demanded to reduce the electric power consumption of the temperature control device as small as possible. For example, the optical fiber module is demanded to reduce the maximum electric power consumption to five watts or below in the range of temperature for use.
In order to realize the reduced electric power consumption, various package structures have been devised. For example, an invention titled by METHOD FOR PACKAGING HEATER-HEATED OPTICAL WAVEGUIDE AND ITS PACKAGE is proposed in a Japanese Patent Application (JP-A-11-014844). The proposal submits the configuration that an optical component is floated and housed inside a package interposing one to four poles. The proposal forms the thickness of the package to be 22 mm, satisfying the electric power consumption of a heater at five watts or below.
The proposal submits a method that the area of the surface to fix the poles is set to 0.03 to 1.0 cm2, and the contact area of the optical component to the poles and the contact area of the poles to the package are reduced, whereby the electric power consumption of the heater is reduced.
In the meantime, the optical fiber modules built in an optical communication system unit is demanded to reduce the dimensions (thickness). Then, to meet the demand, the inventor decided to fabricate the optical fiber module of a following sample fabrication 1 as shown in FIG. 13 in which the thickness of the package 2 (A shown in FIG. 13) was reduced to 12 mm below being the requirement of the system side.
The optical fiber module of the sample fabrication 1 is the optical fiber module adapting the configuration of the proposal, which is formed to overlay an optical component 1, a heat spreading plate 22, and a temperature control device 5 one by one. The temperature control device 5 is formed of a heater.
A resistance temperature device is mounted on the heat spreading plate 22. The resistance temperature device is disposed for sensing the temperatures of the optical component 1. On the lower side of the heat spreading plate 22, poles 30 are disposed at four corners. The thickness of the air space between the top face of the optical component 1 and the cover part 2b of the package 2 (B shown in FIG. 13) is two millimeters. In addition, the thickness of the air space between the bottom face of the heat spreading plate 22 and the package main body 2a of the package 2 (Bxe2x80x2 shown in FIG. 13) is two millimeters as well.
Table 1 shows the component configuration of the optical fiber module of the sample fabrication 1. In Table 1, the resistance of the resistance temperature device is a value at a temperature 0xc2x0 C., and the size of the pole indicates the contact area of the top face of a single pole 30 to the heat spreading plate 22.
In the sample fabrication 1, the package 2 was formed of polyethylene terephthalate (PET) resin having small thermal conductivity. The inventor thought that this configuration would allow reducing the ratio of the heat in the optical component 1 to be released out of the package 2 to decrease the electric power consumption of the temperature control device, the optical component 1 being heated by the temperature control device such as the heater.
The electric power consumption of the temperature control device 5 in the optical fiber module of the sample fabrication 1 was measured, and the electric power consumption was 5.31 W where the ambient temperature was set at a temperature of 0xc2x0 C. and the preset temperature of the optical fiber module was set at a temperature of 80xc2x0 C. The electric power consumption value exceeded five watts demanded by the system side.
In addition, even in the configuration shown in FIG. 13, the electric power consumption can be reduced to five watts or below when the thickness of the air space inside the optical fiber module is thickened without changing the wall thickness of the package main body 2a and the cover part 2b of the package 2. More specifically, when the thickness of the air space between the top face of the optical component 1 and the package 2 (B shown in FIG. 13) and the thickness of the air space between the bottom face of the heat spreading plate 22 and the package 2 (Bxe2x80x2 shown in FIG. 13) are set to seven millimeters, the electric power consumption can be reduced to five watts or below.
However, the optical fiber module having formed the B and Bxe2x80x2 shown in FIG. 13 to be seven millimeters has a greater thickness of 22 mm. Accordingly, the optical fiber module cannot satisfy the demand of scaling down by the system side, that is, the demand is that the thickness of the package 2 shown in A in FIG. 13 is reduced to 12 mm or below.
To further reduce the electric power consumption, the inventor fabricated a sample fabrication 2 in the configuration of the proposal in which the heat spreading plate 22 between the optical component 1 and the temperature control device 5 was omitted as the traditional dimensions (the package thickness of 22 mm) were not changed. The optical fiber module of the sample fabrication 2 has the configuration shown in FIGS. 14A and 14B.
A temperature control device 5 is disposed on the lower side of an optical component 1. Here, the temperature control device 5 is formed of a heater. A temperature sensing element 40 for sensing the temperatures of the optical component 1 is disposed on the upper side of the optical component 1. The temperature sensing element 40 is formed of a resistance temperature device.
The component configuration of the optical fiber module of the sample fabrication 2 illustrated in FIGS. 14A and 14B is as shown in Table 2. In the sample fabrication 2, the contact area of the poles 30 to the optical component 1 and the contact area of the poles 30 to the package 2 were decreased, and the amount of heat conduction from the optical component 1 to the package 2 side was reduced. Accordingly, the electric power consumption of the temperature control device 5 was allowed to be 4.2 W.
In Table 2, the resistance of the resistance temperature device is the value at a temperature of 0xc2x0 C., and the size of the pole is the contact area of the top face of a single poles 30 to the optical component 1. The measured value of the electric power consumption of the temperature control device 5 is the maximum electric power consumption where the ambient temperature was set to 0 to 70xc2x0 C., and the preset temperature of the optical fiber module was set to 70 to 80xc2x0 C.
However, in the configuration of the optical fiber module of the sample fabrication 2, an impact applied to the package 2 was directly transmitted to the optical component 1 through the poles 30. Thus, there has been a problem that the impact strength is weak.
For example, the inventor conducted the impact test to the optical fiber module of the sample fabrication 2 that an impact was applied to the optical fiber module for 500Gxc3x975 times in the three-axial directions orthogonal to each other. As shown in Table 3, the optical component 1 had cracks or the optical component 1 was broken in every sample of the sample fabrication 2.
It is essential that the optical component as a product must clear the reliability test (here, the impact test (500Gxc3x975 times)), and the optical fiber module with the damaged optical component 1 cannot be used. Moreover, the optical fiber modules having cracks in the optical component 1 have great variations in the insertion loss, and they cannot be used as well. As described above, it has been a serious problem that the optical fiber module has weak impact strength.
The optical fiber module is also demanded that the optical characteristics such as insertion loss are not to be varied even though the optical fibers 3 (3a and 3b) are pulled. However, in the traditional optical fiber modules, the optical fibers 3 (3a and 3b) are fixed to the package 2 with the adhesive 23. When the optical fibers 3 (3a and 3b) are pulled, a stress is applied to the optical fibers 3 (3a and 3b) and the connecting parts of the optical fibers 3 (3a and 3b) to the optical component 1 inside the package 2.
The package 2 of the optical fiber module is formed of materials having a greater thermal expansion coefficient such as metals and plastics, which is greatly expanded and contracted by temperature changes more than the configuration members of the optical component 1 and the optical fibers 3 (3a and 3b). Then, with this expansion and contraction, a stress is applied to the optical fibers 3 (3a and 3b) fixed to the package 2. This stress is also applied to the optical component 1 bonded and fixed to the optical fibers 3 (3a and 3b).
When it is done, the influence of the stress has particularly caused an increase in the insertion loss of the connecting parts of the optical component 1 to the optical fibers 3 (3a and 3b).
Because of the applied stress, the connecting parts of the optical component 1 to the optical fibers 3 (3a and 3b) might be damaged, and the optical component 1 might be peeled off from the heat spreading plate 22 according to the circumstances in the configuration of disposing the heat spreading plate 22 as the sample fabrication 1. Therefore, in the traditional optical fiber modules, problems have arisen that the performance is deteriorated by repeating temperature changes and lifetime is shortened.
The inventor observed that the humidity resistance characteristics of the optical fiber modules were not excellent when the package 2 was formed of polyethylene terephthalate resin having small thermal conductivity in order to reduce the electric power consumption of the temperature control device 5 as the optical fiber modules of the sample fabrications 1 and 2.
More specifically, it was revealed that when the package 2 formed of polyethylene terephthalate resin is placed under a high temperature, high humidity environment, the package 2 is deteriorated to affect the characteristics of the optical component 1 inside the package 2.
For example, the inventor allowed the optical fiber module shown in FIGS. 12A to 12C to stand under an environment at a temperature of 85xc2x0 C. at a humidity of 85% for 2000 hours. Consequently, cracks were generated in the package 2 after 2000 hours as shown in Table 4.
As shown in Table 4, when the packages 2 were formed of ABS (acrylnitrile-butadiene-styrene) copolymer, polyacetal resin, and paper bakelite, the same results were obtained. More specifically, the packages 2 formed of these materials were allowed to stand under the environment at a temperature of 85xc2x0 C. at a humidity of 85% for 2000 hours, and then cracks were generated after 2000 hours.
As described above, when the cracks are generated in the package 2 under the high temperature, high humidity environment, the characteristics of the optical component 1 inside the package 2 are deteriorated, which causes a serious problem.
In one aspect, the invention is to provide a following optical fiber module. More specifically, the optical fiber module of the invention has:
a package;
an optical component housed inside the package; and
optical component holding parts disposed between the optical component and the package for holding the optical component,
wherein a configuration of holding the optical component by the optical component holding part has a configuration of reducing heat conduction for reducing the heat conduction between the optical component and the package.